Plastic pipe bending jig

ABSTRACT

A process and jig for field bending relatively large diameter plastic pipe, the jig being to guide the pipe at the point of tangency adjacent the bend after the pipe is heated and bent to form a smooth curvature to the desired radius and degree of bend as determined by the jig. The jig includes a two-piece spreader tube and a right and left hand guide, each adjustable in width, angle and spacing. The guides are U-shape and extend beneath the spreader tube so that the pipe may be placed on a flat horizontal surface. Each guide is provided with a protractor, one of which includes an offset scale so that offsets or curves with generally parallel tangents may be formed. The spreader tube includes a scale to ascertain the chord in terms of the radius for given degrees of bend.

BACKGROUND OF THE INVENTION

This invention relates generally as indicated to a process and jig forfield forming relatively large diameter plastic pipe or conduit. Theinvention of this application represents certain improvements in plasticpipe bending jigs of the type shown in applicants' prior U.S. Pat. No.3,776,539 issued Dec. 4, 1973.

In applicants' above noted prior patent, there is illustrated severalforms of a plastic pipe bending jig, at least one of which has provenuseful in the field forming of relatively small diameter plastic pipe ortube. Since plastic pipe must be heated to be bent, and since heatedplastic pipe is generally like wet spaghetti, it is important that thepipe or tube, particularly when of a larger diameter, be placed andmaintained on a substantially flat and dry surface. Even the slightestirregularity can cause an undesired deformation in the pipe or tube tobe bent. For large size conduit in the range of from about 2 to about 6inches in diameter, such conduit, especially when heated, is difficultto support, carry or transport. It is thus easier to provide a jig whichincludes guides which may be positioned over the pipe. It is accordinglyimportant that the jig be of light weight and yet sturdy construction.Moreover, it should be readily capable of being assembled in the field,and when assembled readily adjustable to form the desired bend in theparticular size conduit involved.

The jig of the present invention provides a two-piece spreader tube anda right and left hand linear guide, each guide being adjustable inwidth. The angle of the guide and the spacing of such guides on thespreader tube is readily determinable and capable of selection. Eachguide is readily adjustable in width to accommodate the conduitdiameters noted above and each guide is provided with a protractorreadily clamped to the spreader tube, the protractor of one guideincluding an offset scale so that offsets or curves with generallyparallel tangents may be formed. The spreader tube includes a scale toascertain the chord of the curve in terms of the radius for givendegrees of bend.

The spreader tube may be disassembled and the guides disassembled fromthe spreader tube so that the components of the bending jig may beplaced in a compact fashion as a kit in a carrying box.

It is a principal object of the present invention to provide a jig forthe field bending of relatively large diameter plastic conduit which maybe assembled and disassembled to form a readily transportable andlightweight kit.

Another principal object is the provision of a field kit for theformation of bends in plastic pipe which includes two linear guidesmounted beneath a spreader bar with the width of the guides beingreadily adjustable through a substantial range.

Another important object is the provision of such jig for bendingrelatively large diameter plastic pipe wherein the guides are pivotedeach to a protractor in turn clamped to the spreader tube so that theangular inclination of the guide with respect to the tube may readily beset.

Yet another important object is the provision of such jig wherein thespreader tube includes a scale by which the spacing of the guides may beobtained, such scale setting the chord of the bend in terms of theradius for certain given degrees of bend.

Another object is the provision of a lightweight easily assembled jigfor the field bending of plastic pipe.

Still another object is the provision of a method for field formingbends in plastic pipe which includes the steps of placing first one setlinear guide over the pipe and then the other after the pipe is broughtto the desired degree of curvature on a flat surface.

Other objects and advantages of the present invention will becomeapparent as the following description proceeds.

To the accomplishment of the foregoing and related ends the invention,then, comprises the features hereinafter fully described andparticularly pointed out in the claims, the following description andthe annexed drawings setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however, of but afew of the various ways in which the principle of the invention may beemployed.

BRIEF DESCRIPTION OF THE DRAWINGS

In said annexed drawings:

FIG. 1 is a perspective view of the jig of the present inventionconfining a plastic conduit in turn supported on a flat surface;

FIG. 2 is a view similar to FIG. 1 illustrating the jig employed to formoffsets in the conduit;

FIG. 3 is an enlarged top plan view of the left hand guide as seen inFIGS. 1 and 2;

FIG. 4 is an end elevation of such guide as seen from the line 4--4 ofFIG. 3;

FIG. 5 is an isometric view of the two L-shape components interconnectedwith the top horizontal legs thereof extending toward each other toaccommodate larger size conduits;

FIG. 6 is a view similar to FIG. 5 illustrating the components assembledwith the horizontal legs thereof extending in the same direction toaccommodate conduits of smaller size;

FIG. 7 is a top plan view of the protractor of the right hand guide inFIGS. 1 and 2 clamped to the spreader tube; and

FIG. 8 is a broken illustration of the label or decal placed on eachsection of the spreader tube to convert the radius to the chord for theindicated given degrees of bend.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, there is illustrated a jig 10 in accordancewith the present invention confining plastic conduit 11 to form thecurvature 12 therein.

The jig comprises left and right hand guide assemblies indicated at 14and 15 which are adjustable width inverted U-shape linear guides whichclosely conform to the O.D. of the conduit 11 and confine the same atthe point of tangency of the curvature 12. Both the jig and the conduitare supported on a flat surface 16 while the conduit, heated to form thebend, cools and rigidifies.

Each guide assembly comprises L-shape guide sections 18 and 19, each ofwhich includes vertical legs seen at 20 and 21, respectively, as seenmore clearly in FIGS. 4, 5 and 6. Each also includes a horizontal topleg as seen at 22 and 23, respectively. The top leg of the section 19 issomewhat shorter and is provided with edge flanges 25 and 26 whichterminate in horizontal flanges 27 and 28 forming, with the top leg 23,channel shape guides closely accommodating the edges of the top leg 22of the section 18.

Each channel thus formed is provided with a tapped aperture and a weldnut indicated at 30 so that thumb screws seen at 31 may be employed toclamp the two horizontal legs of the guide sections together to precluderelative movement once the width setting desired is obtained.

As seen in FIG. 5, the two guide sections may be assembled with thehorizontal legs directed toward each other to obtain width settings of,for example, 5 to 6 inch conduit, while in FIG. 6 they may be assembledwith the horizontal legs in the same direction for width settings of,for example, 2 to 4 inch conduit. As seen in FIGS. 3-6, the top leg 22of the section 18 is provided with an aperture 33 through which thethreaded stud 34 of protractor 35 projects. The stud may be secured tothe horizontal wall 22 by means of a nut 36. The nut 36 is preferablypermanently fixed in place with insufficient clamping pressure topreclude the protractor 35 from pivoting with respect to the horizontalwall 22 of the section 18 about the axis of the stud 34.

The protractor 35 comprises a horizontal plate 37 which includes arectangular elongated portion 38 supporting upwardly projecting spreadertube clamps 39 and 40, each of which include upwardly extending springfingers 41 and 42 which are pulled together by the thumb screw 43 onstud 44 which extends between the distal ends of the fingers.

The major part of the plate 37 is upwardly offset as indicated at 46 toprovide a clearance for the top flanges 27 and 28 of the channel guidesfor the L-shape section 19. The upwardly offset portion of the plate isformed into a circular segment, the radius of the circle being struckfrom the center of the stud 34. An arcuate slot 48 is provided in theplate and has the same center.

As seen perhaps more clearly in FIG. 5, a stud 50 projects upwardly fromthe horizontal leg 22 of the L-shape section 18, such stud projectingfrom a dimpled or offset portion of the horizontal leg as indicated at51. This provides clearance for the head of the stud beneath the leg topermit the horizontal leg 23 to slide therebeneath. The dimple alsoprovides a clamping abutment. An index tab 52 also projects upwardlyfrom the top surface of leg 22. Both the stud and the index tab projectthrough and are within the arcuate slot 48. A shouldered thumb nut 53 isprovided on the stud 50 and is employed to clamp the protractor and thehorizontal leg 22 of the section 18 together in the desired angularrelationship as determined by the index tab 52 which is used to read thescale 54 on the protractor adjacent the slot 48. Such scale includes a0° indicia as indicated at 55. When the marker is on the 0° indicia asindicated, the guide 14 is parallel to the spreader tube 56 passingthrough the clamps 39 and 40. On one side of the 0° indicia, the scaleincludes six markings indicating 15°, 30°, 45°, 60°, 75° and 90°, suchmarkings extending over a 45° span of the arc of the slot. The slotextends beyond the 90° indicia as indicated at 57 to accommodate thestud 50 when the marker or tab 52 is opposite the 90° index mark.

On the opposite side of the 0° mark 55, the scale is divided equally inthree increments with the 30°, 60° and 90° indicia as shown. In thismanner the left hand guide may be pivoted 45° on either side of aposition parallel to the spreader bar 56. The portion of the scaleincluding the 0, 15, 30, 45, 60, 75 and 90° marks is used for formingbends as seen in FIG. 1 while the scale on the opposite side of 0°indicated at 58 is used for forming offsets as seen in FIG. 2. Theprotractor for the right hand guide 15, as seen in FIG. 7, includes aplate 59 slidably clamped to the spreader tube 56 by the clamps 60 and61 and includes the arcuate slot 62 which has the 0°-90° scale over 45°but does not include the offset scale as in the left hand protractor.The construction of the right hand guide, aside from the righthandedness of the L-shape sections and the protractor plate, is the sameas for the left hand guide seen in detail in FIGS. 3 and 4.

Referring again to FIGS. 1 and 2, it will be seen that the spreader tube56 includes two equal length parts 64 and 65 which are interconnected bythe threaded coupling shown generally at 66. Such coupling may comprisea fixed plastic element 67 on the end of the spreader tube right handsection 65 which includes a projecting male threaded element. A similarplastic female threaded element 68 is rotatably mounted on the end ofthe left hand spreader tube section 64 so that the sections may readilybe assembled and disassembled. The plastic fittings are provided withridges as seen at 69 in FIG. 2 readily to permit the sections to beassembled and tightened and then disassembled. Since the sections areeach over 40 inches long, the disassembly permits the packing of theindividual sections in a much shorter kit for storage andtransportation. The guides 14 and 15 can, of course, be readilyassembled and disassembled on the spreader tube by means of the clampsshown.

Referring now to FIG. 8, each spreader tube section is provided with ascale which may be applied as an adhesive decal, the scale for the lefthand spreader tube section 64 being shown foreshortened at 72 in FIG. 8.The scale on the right hand spreader tube section 65 will besymmetrically reversed in form. Each scale actually comprises sixdifferent parallel scales, there being one scale for each of theincrements on each protractor at 15, 30, 45, 60, 75 and 90°. Each scaleexpresses for its selected degrees of bend the radius of curvature asthe sine of one half the angle of curvature. For example, the 18 inchmark on the respective scales reading from 15° to 90° is indicated at73, 74, 75, 76, 77 and 78, respectively. The 15° blend scale may extendfrom 18 inches to 72 inches, the 72 inch marker being indicated at 79.Thus each large marker represents an increment of 6 inches. The 30° bendscale may extend from 12 inches to 72 inches, each large marker againrepresenting an increment of 6 inches. The 45° bend scale may extendfrom 12 inches to 72 inches. The 60° bend scale may extend from 12inches to 66 inches. The 75° bend scale may extend from 12 inches to 54inches, while the 90° bend scale extends from 12 inches to 48 inches. Inany event, the scale is to be read as the selected radius of curvaturefrom the inside of the conduit or pipe 11 while it actually representsone half the chord.

In operation the two-piece spreader tube may be removed from itscarrying case and the threaded fitting 66 engaged so that the twosections of the spreader tube are clamped together. The two sectionsshould be connected so that the printed scales thereon are facing theoperator. The left and right hand guides are inserted on the respectiveends of the spreader tube as assembled and they may be spread therealongto any desired position. The jig is then ready to preset for any radiusand any segment of bend.

To set the jig for the selected bend, the inside radius and the degreesof bend required should be determined and this can be obtained fromTable 346-10, of the National Electric Code for Minimum Radius.

The L-shape sections of the guides are then adjusted and locked as seenin FIGS. 5 and 6 for the size conduit to be formed. A close fit over theconduit is important.

Next the user sets and locks the degrees of bend on both the left andright hand conduit guide protractors. For example, both may be set andlocked at 45°. The operator then selects the correct "degrees of bend"scale on the spreader tube. The operator then slides the left and rightconduit guides to the desired inside radius as read on the selectedscale. The edge indicated at 82 in FIG. 3 and 83 in FIG. 7 may be usedto line up the guide with the appropriate inside radius index line onthe selected scale for the selected angle of bend. The locking knobs orclamp nuts 43 are now tightened to secure the guides at the properposition.

Now, to form the bend, the ends of the pipe or conduit section to beformed may be provided with expansible plugs as seen at 85 and 86 inFIG. 1, and the conduit then placed in a heater which uniformly heatsthe section desired to be bent. The plugs serve to trap air inside theconduit to prevent the wall from buckling upon formation of the curve.The heater air within the interior of the conduit creates a pressure forthis purpose.

The plugged heated conduit is then removed from the heater and placed onthe dry flat surface 16. The jig is then picked up as though one werelifting a barbell and lowered over the conduit so that one conduit guideslides over the conduit at the point where the bend is to begin. Forexample, the right hand guide 15 may initially be placed over the heatedconduit. The operator may then pull the free end of the heated conduitto form a smooth curve and lift the empty conduit guide section 14 usingthe end of the spreader tube as a handle to place the same over the nowformed conduit. The bend may now be set by sponging with cold water.

To form offsets such as seen in FIG. 2, the left hand conduit guide maybe set at the desired 30, 60 or 90° indication on the offset scale 58.The right hand conduit guide may be set on its scale on the same degreeof bend so that the conduit guides are parallel. The desired distance ofthe offset can now be obtained by adjusting the distance between theconduit guides. The curvature and dimension of the offset can be variedby the use of different degree settings of the protractors and thedistance between the conduit guides. The scale on the spreader tube doesnot apply when forming offsets. To form the offset, the steps of formingthe bend described above are repeated.

The jig for accomplishing the bending steps outlined above is quitesturdy yet relatively lightweight. For example, the protractor and theL-shape sections of each guide may be formed of 18 gauge steel and theedges of the L-shape sections may be folded and flattened as indicated.Preferably the parts are plated. The various elements of the jig mayreadily be assembled and disassembled for storage and transportation.

Other modes of applying the principles of the invention may be employed,change being made as regards the details described, provided thefeatures stated in any of the following claims or the equivalent of suchbe employed.

We claim:
 1. A jig to facilitate the formation of a curvature in arelatively large diameter plastic pipe comprising an elongated support,a pair of protractors slidably mounted on said support, and adjustablewidth linear guides pivoted to each protractor to hold the pipe beyondthe ends of such curvature to establish linear segments of the pipebeyond such ends, means adjustably to lock each protractor to saidsupport to vary the distance therebetween on said support and thus thedistance between such linear segments, and means adjustably to lock eachlinear guide to its respective protractor to vary the angularrelationship of said guides and thus such linear segments relative toeach other.
 2. A jig as set forth in claim 1, wherein said support istubular and is formed of two pieces interconnected end-to-end ofsubstantially the same length.
 3. A jig as set forth in claim 1, whereineach protractor includes clamp means to fix the same with respect tosaid support.
 4. A jig as set forth in claim 1, wherein one protractorincludes a scale of from 90° to 0°, on a 45° arc, while the otherincludes a scale of from 90° to 0° to 90° on a 90° arc.
 5. A jig as setforth in claim 1, wherein each guide includes two inverted L-shapeparts, the horizontal legs of which are slidably interconnected to varythe spacing between the vertical legs thereof.
 6. A jig as set forth inclaim 5, wherein one L-shape part has a shorter horizontal leg than theother and includes channels adapted to receive the horizontal leg of theother, and clamp means in said channels adapted adjustably to lock saidparts together.
 7. A jig as set forth in claim 5, wherein said L-shapeparts may be assembled with the horizontal legs extending in the samedirection for pipes of relatively small diameter, or with the horizontallegs extending in the opposite direction for pipes of larger diameter.8. A jig as set forth in claim 5, wherein one of said parts has itshorizontal leg pivoted to its respective protractor and includes a studprojecting through an arcuate slot in said protractor, said slot beingstruck from said pivot.
 9. A jig as set forth in claim 8, including aclamp nut on said stud, and an angle indicator projecting from saidhorizontal leg into said slot and offset from said clamp nut.
 10. A jigto facilitate the formation of a curvature in a relatively largediameter plastic pipe comprising an elongated linear support, a pair ofguides for holding the pipe beyond the ends of such curvature mounted onsaid support for sliding movement therealong, means supporting each saidguide on said support for swinging movement to a selected angle,symmetrically reversed scale means on said support, one for each guide,each scale means including a plurality of parallel scales to indicatethe position of the guides along said support for determining a selectedradius and angle of curvature of the pipe.
 11. A jig as set forth inclaim 10, including a plurality of parallel scale means, one for each ofa selected angle of curvature.
 12. A jig as set forth in claim 11,wherein each scale provides a setting of the chord expressed as ameasure of the inside radius of the curvature of the pipe for theselected angle of curvature.
 13. A jig as set forth in claim 10, whereinsaid support includes two separable equal length halves, each halfincluding a series of scales thereon, each for a plurality of selectedangles of curvature, each scale expressing the radius of curvature asthe sine of one half the angle of curvature.
 14. A jig as set forth inclaim 10, wherein said support comprises two equal length interconnectedsections each including a scale to determine the chord of the curvaturefrom the radius of curvature for a selected angle of curvature.